CN109374089A - The optical fiber sensing system and its measurement method that liquid level and fluid temperature measure simultaneously - Google Patents
The optical fiber sensing system and its measurement method that liquid level and fluid temperature measure simultaneously Download PDFInfo
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- CN109374089A CN109374089A CN201811475569.8A CN201811475569A CN109374089A CN 109374089 A CN109374089 A CN 109374089A CN 201811475569 A CN201811475569 A CN 201811475569A CN 109374089 A CN109374089 A CN 109374089A
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- 230000035559 beat frequency Effects 0.000 claims description 15
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
- G01F23/28—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
- G01F23/284—Electromagnetic waves
- G01F23/292—Light, e.g. infrared or ultraviolet
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Thermal Sciences (AREA)
- Fluid Mechanics (AREA)
- Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)
- Measuring Temperature Or Quantity Of Heat (AREA)
Abstract
The optical fiber sensing system and its measurement method measured simultaneously the invention discloses a kind of liquid level and fluid temperature, optical fiber sensing system includes screw thread package tube, microstructured optical fibers and coherent phase demodulating equipment, wherein in the thread groove of microstructured optical fibers insertion screw thread package tube, one end is connected into coherent phase demodulating equipment, and the other end is connected into surveyed liquid；Screw thread encapsulation pipe surface is coated with one layer of flexible glue for packaging protection microstructured optical fibers；Coherent phase demodulating equipment is used to demodulate the distributed sensing signal in microstructured optical fibers, measures the temperature-responsive of each independent sensing section in microstructured optical fibers, calculates liquid level and fluid temperature.The present invention is according to the sensing section coarse localization liquid level of liquid level temperature jump position, it is accurately positioned liquid level further according to sensing section phase change and the relationship of liquid level, realizes that full distributed sensing, system response dynamics range are big, the response of measurement accuracy height is fast, applied widely.
Description
Technical field
The present invention relates to sensory field of optic fibre, the optical fiber measured simultaneously more particularly, to a kind of liquid level and fluid temperature
Sensor-based system and its measurement method.
Background technique
Liquid level and temperature monitoring in the fields such as petroleum transportation and storage, chemical process, flood warning, wastewater treatment very
It is important.For example, the accurate measurement of liquid level and oil storage temperature can understand production inventory situation in real time in oil storage tank, guarantee peace
Complete steady production and storage influence stock control and economic transactions very big.The liquid level sensor of mainstream is all based on electricity at present
Sensing.For example, existing capacitance type sensor needs for metal capacitance plate and metal line to be placed in tank.This electrical cloth
Line needs careful shielding, engagement and ground connection, to reduce parasitic capacitance, and further requirement periodic maintenance to the greatest extent, to ensure electricity
The integrality of gas contact.Secondly, capacitance probe measurement also needs temperature sensor to input, to improve level gauging accuracy, and
And under inflammable and explosive environment, once electric transducer breaks down, it is easy to cause safety accident.
Fibre optical sensor due to small in size, corrosion-resistant, electromagnetism interference, be easy to networking multiplexing the features such as, can be severe
Normal use in environment is got more and more attention in sensor field.Existing fibre optic liquid level sensor is based primarily upon optical interference
The problem of structure or fiber grating etc., it is small that there are measurement ranges, and measurement accuracy is easily affected by the external environment, it usually needs carry out
Temperature-compensating is to improve the accuracy of level gauging.
Summary of the invention
In view of the drawbacks of the prior art, the present invention proposes the optical fiber sensing system of a kind of liquid level and fluid temperature while measurement
And its measurement method, it is intended to solve that existing fiber liquid level sensor measurement range is small, and measurement accuracy is easily affected by the external environment, survey
The not high problem of accuracy of measurement.
To achieve the above object, the present invention provides the optical fiber sensing system that a kind of liquid level and fluid temperature measure simultaneously,
Including screw thread package tube, microstructured optical fibers and coherent phase demodulating equipment.The thread groove of microstructured optical fibers insertion screw thread package tube
In, one end is connected into coherent phase demodulating equipment, and the other end is connected into testing liquid；Screw thread package tube is embedding in microstructured optical fibers
Surface after entering is coated with one layer of flexible glue for packaging protection microstructured optical fibers, and screw thread package tube is also used to improve liquid level and temperature is surveyed
The spatial resolution and sensitivity of amount；Coherent phase demodulating equipment is used to demodulate the distributed sensing signal in microstructured optical fibers,
The temperature-responsive for measuring each independent sensing section in microstructured optical fibers, calculates liquid level and fluid temperature.
The present invention measures micro-structure using the distributed sensing signal in coherent phase demodulation method demodulation microstructured optical fibers
The temperature-responsive of each independent sensing section, calculates liquid level and fluid temperature information by temperature demodulation algorithm in optical fiber.?
In level monitoring, since liquid evaporation effect and liquid are different from the specific heat capacity of gas, the gas on gas-liquid contact face will lead to
Mutually and liquidus temperature generates mutation.Corresponding sensing section is found using the position of fibre optic temperature sensor measurement temperature jump
Realize quasi-distributed level monitoring.Further, the sensing section at liquid level can be divided into two portions in gas neutralising fluid
Point, the temperature field of described two parts can be considered uniformly in short distance, immerse liquid depth and the sensing according to optical fiber
The linear relationship for the phase value that section measures, liquid level can be further accurately positioned, and realize full distributed level monitoring.Temperature measurement
In, due to containing multiple closely coupled independent sensing sections in the microstructured optical fibers, the sensing section in liquid can
To realize the distributed fluid temperature measurement of different depth.Further, the high sensitivity of microstructured optical fibers and overlength are utilized
The characteristic of distance sensing is, it can be achieved that high-precision liquid level and fluid temperature monitoring on a large scale.
Preferably, multiple scattering enhancing points mention on microstructured optical fibers for enhancing the backscatter signals of sensor fibre
High system signal noise ratio, scattering enhance the connection optical fiber between point as sensitive zones, and microstructured optical fibers are divided by scattering enhancing point
Multiple independent sensing sections.
Preferably, scattering enhancing point is generated on counter-bending single mode optical fiber by uv-exposure, and all scatterings enhance point
Equidistant arrangement, and the reflectivity of the scattering enhancing point is -50dB~-40dB.
Preferably, screw thread package tube is made by processing thread groove on hard material, and the spacing and depth of thread groove are big
In microstructured optical fibers diameter.
Preferably, coherent phase demodulating equipment includes light source module, optical modulator module, coherent reception module and digital signal
Processing module；Light source module is for generating continuous narrow-linewidth laser；The input terminal of optical modulator module and the output end of light source module
Connection exports short pulse sequence for continuous narrow-linewidth laser to be carried out shift frequency and modulation treatment；One of coherent reception module
The output end of the connection of the output end of input terminal and light source module, another input terminal and microstructured optical fibers connects, for allowing reference
Light and backscattering light pulse subsequence interfere to form beat frequency optical signal subsequence, and beat frequency optical signal subsequence is converted
For electric signal, and export beat frequency subsequence；The input terminal of digital signal processing module is connect with the output end of coherent reception module,
For beat frequency subsequence to be carried out phase demodulating.
As another aspect of the present invention, the present invention provides the Fibre Optical Sensors that a kind of liquid level and fluid temperature measure simultaneously
The measurement method of system, detection light through frequency displacement and are modulated into multiple short pulse sequences, and each short pulse is in microstructured optical fibers
Short pulse subsequence is formed through multiple scatterings enhancing point reflection, backscattering light pulse subsequence and the reference light of return enter phase
Dry receiving module interferes to form beat frequency optical signal subsequence, obtains the strong of beat frequency optical signal subsequence by relevant detection
Then degree demodulates the phase change between adjacent scattering enhancing point by cross-correlation method, and is restored by phase unwrapping
It is last to obtain liquid level and fluid temperature simultaneously to the phase information in inductive sensing section.Cross-correlation method passes through cross correlation algorithm
To obtain, subsequence signal is corresponding to scatter the sensing section enhanced between point to the waveform of adjacent subsequence in processing reflected light signal
Phase information.
Preferably, the duration of each short pulse is in backscattering light pulse sequenceTwo adjacent short arteries and veins
The interval of punchingWherein, n is microstructured optical fibers refractive index, and L is the spacing of scattering enhancing point in microstructured optical fibers, N
For the scattering enhancing point number in microstructured optical fibers, c is the light velocity.It is non-overlapping between each back-scattering light signal subsequence, then
Each back-scattering light signal subsequence and the beat frequency optical signal subsequence that continuous narrow-linewidth laser generates be not be overlapped, improves number
Signal processing module increases the response frequency range of optical fiber sensing system to the demodulation rate of beat frequency electric signal.
The measurement method for the optical fiber sensing system that a kind of liquid level provided by the invention and fluid temperature measure simultaneously further includes
Due to having temperature jump at liquid-level interface, the maximum sensing section of phase changing capacity is found, this section of phase signal is extractedAnd according to
The position coarse localization liquid level h on screw thread package tube of the sensing section；Extract first be located at below liquid-level interface
Sense the phase signal of sectionExtract the phase signal for first sensing section being located above liquid-level interfaceIt is obtained by formula
Accurate liquid levelWherein l is adjacent after microstructured optical fibers encapsulate on screw thread package tube
Sense the center spacing of section.Before starting measurement, the phase signal of each sensing section is found according to currently known fluid temperature
Phase value corresponding with the temperature, since each phase changing capacity sensed in section and temperature variation are linear, temperature
The temperature information that can be obtained liquid when measurement according to the phase signal for being totally submerged sensing section in a liquid, according to complete
The phase signal of the sensing section in gas can be obtained the temperature information of gas entirely.
Technical solution of the present invention compared with prior art, there is following technical effect:
1, according to the sensing section coarse localization liquid level of liquid level temperature jump position, further, according to sensing section phase
The relationship of position variation and liquid level, is accurately positioned liquid level, realizes full distributed sensing.
2, since microstructured optical fibers contain multiple independent sensing sections, the distribution of different height is may be implemented in the sensor
The measurement of formula liquid level temperature.
3, the cascade that thousands of sensing sections may be implemented using the scattering enhancing point of superweak reflectivity, greatly improves liquid
Position investigative range.
4, due to using coherence detection and cross-correlation method demodulation phase, real-time frequency response range is up to number kHz
And low frequency quasi-static signal can be detected, system response dynamics range is big, it can be achieved that fast-changing liquid level and quasi-static
The level gauging of variation.
Detailed description of the invention
Fig. 1 is the microstructured optical fibers distribution of liquid level provided by the invention and fluid temperature while the optical fiber sensing system of measurement
Schematic diagram；
Fig. 2 is the structural schematic diagram of liquid level provided by the invention and fluid temperature while the optical fiber sensing system of measurement；
Fig. 3 is coherent phase demodulation dress in liquid level provided by the invention and fluid temperature while the optical fiber sensing system of measurement
The structural schematic diagram set；
Fig. 4 is light source module, optical modulator module and coherent reception module in coherent phase demodulating equipment provided by the invention
Structural schematic diagram；
Fig. 5 is level gauging result schematic diagram in the embodiment of the present invention；
Fig. 6 is fluid temperature measurement result schematic diagram in the embodiment of the present invention.
Specific embodiment
In order to make the objectives, technical solutions, and advantages of the present invention clearer, with reference to the accompanying drawings and embodiments, right
The present invention is further elaborated.It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, and
It is not used in the restriction present invention.
The present invention relates to the optical fiber sensing systems that a kind of liquid level and fluid temperature measure simultaneously, as shown in Figure 1, the present embodiment
It include: screw thread package tube, microstructured optical fibers 5 and coherent phase demodulating equipment.Using 248nm ultraviolet laser after light beam focuses
Scattering enhancing point production microstructured optical fibers 5 are inscribed on counter-bending single mode optical fiber, the spacing of adjacent scattering enhancing point is 2m, reflection
Rate is -50dB；Screw thread package tube is made of the aluminum metal tube of outer diameter 20mm, is carved using numerically-controlled machine tool in aluminum metal tube surface
Lower thread groove, the depth of thread groove are 0.3mm, and the spacing of thread groove is 0.3mm；Microstructured optical fibers 5 are embedded in screw thread package tube
In thread groove, one end is connected into coherent phase demodulating equipment, and the other end immerses in testing liquid；Screw thread package tube is in micro-structure
Surface after optical fiber insertion is coated with one layer of flexible glue for packaging protection microstructured optical fibers, screw thread package tube be also used to improve liquid level with
The spatial resolution and sensitivity of temperature measurement；Coherent phase demodulating equipment is used to demodulate the distributed sensing in microstructured optical fibers
Signal measures the temperature-responsive of each independent sensing section in microstructured optical fibers, calculates liquid level and fluid temperature.
As in Figure 2-4, coherent phase demodulating equipment includes light source module 1, optical modulator module 2,3 and of coherent reception module
Digital signal processing module 4；Light source module 1 includes laser light source 11 and the first fiber coupler 12；Optical modulator module 2 includes sound
Optical modulator 21, EDFA Erbium-Doped Fiber Amplifier 22, narrow linewidth bandpass filter 23 and circulator 24, wherein 21 shift frequency of acousto-optic modulator
200MHz, shortest pulse duration 10ns, 20 μ s of pulse spacing；Erbium-doped fiber amplifier 22 is for amplifying detection light, narrow linewidth
Filter 23 is for filtering out detection light with the noise of wave section；Coherent reception module 3 includes the second fiber coupler 31 and balance
Detector 32.Laser light source 11 issues the continuous narrow-linewidth laser that wavelength is 1549.7nm, passes through the first light of splitting ratio 99:1
Fine coupler 12 divides for reference light and detects light, and detection light passes through a mouth of optical circulator 24 after optical modulator module modulation
Input is returned from the output of the b mouth of optical circulator 24 to microstructured optical fibers by each scattering enhancing point on microstructured optical fibers 5
Backscattering light pulse subsequence is inputted by the b mouth of optical circulator 24, is exported from the c mouth of optical circulator 24, splitting ratio 50:
50 the second fiber coupler 31 will be input to balanced detector 32, shape after backscattering light pulse subsequence and reference combiner
At beat frequency and electric signal is exported, the electric signal of 4 pairs of the digital signal processing module acquisitions uses cross-correlation and difference algorithm,
It obtains and senses the phase information of section between adjacent scattering enhancing point, then transducing signal waveform is restored using phase unwrapping algorithm,
The position of transducing signal passes through the short pulse subsequence sequencing received and obtains.The location information of each sensing section can be by every
One short pulse corresponds to corresponding sensing section by the sequencing for the subsequence that different scattering enhancing point reflections return, wherein dissipates
It is fixed in microstructured optical fibers manufacturing process for penetrating the position of enhancing point.
In a particular application, due to having temperature jump at liquid-level interface, the maximum sensing section of phase changing capacity is found, is extracted
This section of phase signalAnd according to the position coarse localization liquid level h on screw thread package tube of the sensing section；Extraction is located at
The phase signal of first sensing section below liquid-level interfaceExtract first sensing section being located above liquid-level interface
Phase signalAccurate liquid level is obtained by formulaWherein l is microstructured optical fibers in spiral shell
The center spacing of neighboring sensor section after being encapsulated on line package tube.As shown in figure 5, liquid level is at the uniform velocity risen with the speed of 0.4mm/s,
Successively pass through 5 sensing sections within the period of 100s to 225s, senses section after the calculating of above-mentioned demodulation method and by 5
After level gauging Data Synthesis, the relationship of liquid level variation and phase change within the scope of 50mm, level gauging sensitivity are obtained
For 26.9rad/mm.And before the start of the measurement, the phase signal of each sensing section is found according to currently known fluid temperature
Phase value corresponding with the temperature, since each phase changing capacity sensed in section and temperature variation are linear, temperature
The temperature information that can be obtained liquid when measurement according to the phase signal for being totally submerged sensing section in a liquid, according to complete
The phase signal of the sensing section in gas can be obtained the temperature information of gas entirely.
The present invention relates to the fluid temperatures of a kind of liquid level and fluid temperature while the optical fiber sensing system of measurement to demodulate example,
As shown in fig. 6, the sensing section in liquid, phase change and temperature changing curve diagram, temperature sensitivity 29.7rad/
℃。
It should be noted last that the above specific embodiment is only used to illustrate the technical scheme of the present invention and not to limit it,
Although being described the invention in detail referring to preferred embodiment, those skilled in the art should understand that, it can be right
Technical solution of the present invention is modified or replaced equivalently, without departing from the spirit and scope of the technical solution of the present invention,
It is intended to be within the scope of the claims of the invention.
Claims (9)
1. the optical fiber sensing system that liquid level and fluid temperature measure simultaneously characterized by comprising screw thread package tube, micro-structure
Optical fiber and coherent phase demodulating equipment；
The microstructured optical fibers are embedded in the thread groove of the screw thread package tube, and one end is connected into coherent phase demodulating equipment,
The other end is for being connected into testing liquid；
Surface of the screw thread package tube after microstructured optical fibers insertion is coated with one layer of flexible glue for packaging protection micro-structure
Optical fiber；
The coherent phase demodulating equipment measures micro-structure for demodulating the distributed sensing signal in the microstructured optical fibers
The temperature-responsive of each independent sensing section, calculates liquid level and fluid temperature in optical fiber.
2. optical fiber sensing system according to claim 1, which is characterized in that there is multiple scatterings to increase on the microstructured optical fibers
Strong point, for enhancing the backscatter signals of sensor fibre, connection optical fiber between the scattering enhancing point as sensitive zones,
Microstructured optical fibers are divided into multiple independent sensing sections by scattering enhancing point.
3. optical fiber sensing system according to claim 2, which is characterized in that the scattering enhancing point is existed by uv-exposure
It is generated on counter-bending single mode optical fiber, the reflectivity of the equidistant arrangement of all scattering enhancing points, the scattering enhancing point is -50dB
~-40dB.
4. optical fiber sensing system according to claim 1, which is characterized in that the screw thread package tube on hard material by adding
Work thread groove is made, and the spacing and depth of the thread groove are greater than microstructured optical fibers diameter.
5. optical fiber sensing system according to claim 1, which is characterized in that the coherent phase demodulating equipment includes light source
Module, optical modulator module, coherent reception module and digital signal processing module；
The light source module is for generating continuous narrow-linewidth laser；
The input terminal of the optical modulator module is connect with the output end of the light source module, for carrying out continuous narrow-linewidth laser
Shift frequency and modulation treatment export short pulse sequence；
One input terminal of the coherent reception module is connect with the output end of the light source module, another input terminal with it is described
The output end of microstructured optical fibers connects, and to form beat frequency light letter for allowing reference light and backscattering light pulse subsequence to interfere
Work song sequence, and electric signal is converted by the beat frequency optical signal subsequence, and export beat frequency subsequence；
The input terminal of the digital signal processing module is connect with the output end of the coherent reception module, is used for the beat frequency
Subsequence carries out phase demodulating.
6. a kind of measurement method based on optical fiber sensing system described in claim 1, which is characterized in that the detection light is through frequency
Multiple short pulse sequences are moved and are modulated into, each short pulse forms in microstructured optical fibers through multiple scatterings enhancing point reflection short
Pulse subsequence, backscattering light pulse subsequence and the reference light of return enter coherent reception module and interfere to be formed
Beat frequency optical signal subsequence obtains the intensity of beat frequency optical signal subsequence by relevant detection, then passes through cross-correlation method solution
The phase change between adjacent scattering enhancing point is recalled, and is restored by phase unwrapping to the phase information in inductive sensing section,
It is last to obtain liquid level and fluid temperature simultaneously.
7. measurement method according to claim 6, which is characterized in that each short arteries and veins in the backscattering light pulse sequence
The duration of punching isThe interval of two adjacent short pulses
Wherein, n is microstructured optical fibers refractive index, and L is the spacing of scattering enhancing point in microstructured optical fibers, and N is in microstructured optical fibers
Scattering enhancing point a number, c is the light velocity.
8. measurement method according to claim 6, which is characterized in that further include extracting liquid level interface phase changing capacity most
The phase signal of big sensing sectionThe phase signal of first sensing section below liquid-level interfaceBe located at liquid level
The phase signal of first sensing section above interfaceAnd it is fixed roughly according to the position of the sensing section on screw thread package tube
Position liquid level h obtains accurate liquid level
Wherein l is the center spacing of the neighboring sensor section after microstructured optical fibers encapsulate on screw thread package tube.
9. measurement method according to claim 6, which is characterized in that further include being found according to currently known fluid temperature
The phase signal phase value corresponding with the temperature of each sensing section, by the phase signal for being totally submerged sensing section in a liquid
The temperature information for obtaining liquid is believed by the temperature change that the phase signal of the sensing section completely in gas obtains gas
Breath.
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| CN113578231A (en) * | 2021-07-07 | 2021-11-02 | 浙江世纪康大医疗科技股份有限公司 | Mechanism and method for preparing liquid preparation containing magnetic liquid particles |
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